Dynamic parameter measurement devices for bicycles have been implemented in various ways. Prior art exists primarily in the measurement of torque and driven wheel angular velocity. Of this prior art, torque measurement and angular velocity have been implemented in the bicycle hub, cranks, chain, pedals, and spokes. All of the prior art references determine angular velocity thru the means of a reed type magnetic switch or a low-resolution optical encoder. Angular velocity measurements taken using such methods provide updates of wheel speed too infrequently to use this data for evaluation of dynamic power applied to the rear wheel during sprint events.
Torque measurement is typically achieved in the prior art thru the use of wire bonded resistive strain gauges. The approach to mounting of these strain gauges in the prior art has typically resulted in measurements, which are subjected to errors due to undesired strains imposed on the particular object to which the gauge is bonded too. Resistive type wire bonded strain gauges perform a point-to-point measurement of the strain, which may not be fully representative of the strain imposed across the entire object being stressed. In addition, these devices require power in order to measure a change in voltage due to strain induced resistance changes.
There has been no evidence of prior art, which claims to measure centripetal acceleration or lateral angular acceleration of the rear driven wheel. It is apparent that measurements of this type would not be possible given the current state of the art in angular velocity apparatus and methods.
The invention disclosed in U.S. Pat. No. 6,418,797 consists of a device, which measures power applied to the rear wheel thru the rear hub of a bicycle. The invention uses resistive wire bond strain gauges and a reed type wheel velocity sensor to determine power applied to the rear wheel. As described previously these methods of measuring torque and wheel velocity cannot determine instantaneous power applied to the rear wheel of a bicycle. In addition implementation of U.S. Pat. No. 6,418,797 implies that a dedicated bicycle wheel is required in order to use the device disclosed in the invention to measure power output of a rider. This prevents the user from easily transferring the device to different wheels of varying sizes. The invention of U.S. Pat. No. 6,418,797 does not provide the user the capability of measuring instantaneous angular acceleration or lateral angular acceleration of the rear driven wheel. It is apparent that the invention described in U.S. Pat. No. 6,418,797 cannot measure dynamic parameters associated with a driven bicycle wheel.
There exists prior art, which appears to have been commercialized before any pending patent applications have either been filed or approved at the time of this writing by the authors. The device is a power measurement device manufactured by Polar Electro, Inc. The device uses a sensor mounted below the chain of a bicycle, which measures the frequency of oscillation of the chain under applied load. This technique is similar to how an individual tunes a guitar string. When load is applied to the chain this changes the 1st natural frequency of the chain under tension. If one knows the mass of the chain and measures this frequency it is relatively simple to determine the tension present in the chain. This method presents problems when the chain has added mass due to containments such as mud, grease, etc. Shifts in natural frequency, which directly influence the computation of chain tension, can occur if added mass is present at the time of data acquisition. In addition the device requires a chain system, which contains significant slack and therefore is not adaptable to single speed-tensioned systems. Velocity measurement is achieved in this system through the use of a pulley, which rides along with the chain. The speed of the pulley is measured through perforated holes in the pulley and a sensing unit, which measures the time at which these perforations pass the sensing unit. This system produces velocity signals, which are proportional and controlled by the rotational speed of the pulley. This limits the maximum sample rate to the speed of the pulley multiplied by the number of perforations. High sample rates are not possible due to hardware limitations of the product. Taking the product of chain tension and chain velocity derives power applied to the chain and hence the rear wheel. The product offered by Polar does not provide the user the capability of measuring instantaneous angular acceleration or lateral angular acceleration of the rear driven wheel or chain. It is apparent that this product offered by Polar cannot measure dynamic parameters associated with a driven bicycle wheel.
The invention disclosed in German Patent DE 3722728 consists of a device, which measures power applied to the cranks of a bicycle. The invention uses resistive wire bond strain gauges and a reed type velocity sensor or a low-resolution encoder to determine power applied to the cranks of a bicycle. As described previously these methods of measuring torque and crank velocity cannot determine instantaneous power applied to the cranks of a bicycle. In addition implementation of German Patent DE 3722728 implies that dedicated bicycle cranks are required in order to use the device disclosed in the invention to measure power output of a rider. This prevents the user from easily transferring the device to different bicycles. The invention of German Patent DE 3722728 does not provide the user the capability of measuring instantaneous angular acceleration or lateral angular acceleration of the bicycle. It is apparent that the invention described in German Patent DE 3722728 cannot measure dynamic parameters associated with a bicycle.
The invention disclosed in U.S. Pat. No. 6,836,711 utilizes a high resolution optical encoder to overcome many of the deficiencies of the prior art. Despite the inventions high resolution optical encoder implementation the invention produces data at the same rate as wheel rotation, thus limiting the maximum achievable sample rate to a integer multiple of the wheel rotation. This severely limits the ability to control the rate at which a user records sensory information. The invention of U.S. Pat. No. 6,836,711 shares the same characteristic problems as the prior art already mentioned in that the hardware selected to measure angular speed dictates the maximum rate at which data can be collected, which is not desirable. This invention claims to measure the rotational displacement of the wheel as a function of time. Thus it is clear to see that two quantities are being measured and used in the computation of angular velocity and angular acceleration. Each of the measured quantities, rotational displacement and time will each have an associated measurement error. In order to compute angular velocity (1st derivative) and angular acceleration (2nd derivative) these independent errors must be propagated through the computations thus resulting in a final product, which is inherently less accurate than the original measurements intended. Further errors could be induced due to the use of a high resolution optical encoder which are susceptible to mounting and alignment induced errors. Implementation of a system like this requires sophisticated calibration routines to ensure the alignment of the device is within specification. Lastly, implementation of this invention requires that the sensor has surfaces that move independently with respect to each other, thus requiring a rotating seal to eliminate containments to the electronics. The invention of U.S. Pat. No. 6,836,711 does not provide the user the capability of measuring torque generated or instantaneous lateral angular acceleration of the bicycle; therefore it is impossible to compute applied power to the driven wheel. It is apparent that the invention described in U.S. Pat. No. 6,836,711 cannot measure all dynamic parameters associated with a bicycle driven wheel.